1. Field of the Invention
The present invention relates in general to the field of data processing. In one aspect, the present invention relates to a method and system for managing clock functions in a communications processor during operation in a low-power mode.
2. Related Art
In general, data processors are capable of executing a variety of instructions. Processors are used in a variety of applications, including communication systems formed with wireless and/or wire-lined communication devices. Such communication systems range from national and/or international cellular telephone systems to the Internet to point-to-point in-home wireless networks. Each type of communication system is constructed, and hence operates, in accordance with one or more communication standards. For instance, wireless communication systems may operate in accordance with one or more standards including, but not limited to, IEEE 802.11, Bluetooth, advanced mobile phone services (AMPS), digital amps, global system for mobile communications (GSM), code division multiple access (CDMA), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS) and/or variations thereof.
Especially with wireless and/or mobile communication devices (such as a cellular telephone, two-way radio, personal digital assistant (PDA), personal computer (PC), laptop computer, home entertainment equipment, etc.), the processor or processors in a device must be able to run various complex communication programs using only a limited amount of power that is provided by power supplies, such as batteries, contained within such devices. In particular, for a wireless communication device to participate in wireless communications, the device includes a built-in radio transceiver (i.e., receiver and transmitter) or is coupled to an associated radio transceiver (e.g., a station for in-home and/or in-building wireless communication networks, RF modem, etc.).
To implement the transceiver function, one or more processors and other modules are used to form a transmitter which typically includes a data modulation stage, one or more intermediate frequency stages and a power amplifier. The data modulation stage converts raw data into baseband signals in accordance with a particular wireless communication standard. The intermediate frequency stages mix the baseband signals with one or more local oscillations to produce RF signals. The power amplifier amplifies the RF signals prior to transmission via an antenna. In direct conversion transmitters/receivers, conversion directly between baseband signals and RF signals is performed. In addition, one or more processors and other modules are used to form a receiver which is typically coupled to an antenna and includes a low noise amplifier, one or more intermediate frequency stages, a filtering stage and a data recovery stage. The low noise amplifier receives inbound RF signals via the antenna and amplifies them. The intermediate frequency stages mix the amplified RF signals with one or more local oscillations to convert the amplified RF signal into baseband signals or intermediate frequency (IF) signals. The filtering stage filters the baseband signals or the IF signals to attenuate unwanted out-of-band signals to produce filtered signals. The data recovery stage recovers raw data from the filtered signals in accordance with the particular wireless communication standard.
In addition to the complexity of the computational requirements for a communications transceiver, such as described above, the ever-increasing need for higher speed communications systems imposes additional performance requirements and resulting costs for communications systems. In order to reduce costs, communications systems are increasingly implemented using Very Large Scale Integration (VLSI) techniques. The level of integration of communications systems is constantly increasing to take advantage of advances in integrated circuit manufacturing technology and the resulting cost reductions. This means that communications systems of higher and higher complexity are being implemented in a smaller and smaller number of integrated circuits. For reasons of cost and density of integration, the preferred technology is CMOS. To this end, digital signal processing (“DSP”) techniques generally allow higher levels of complexity and easier scaling to finer geometry technologies than analog techniques, as well as superior testability and manufacturability.
Because of the computational intensity (and the associated power consumption by the processor(s)) for such transceiver functions, it is an important goal in the design of wireless and/or mobile communication devices to minimize processor and other module operations (and the associated power consumption). One way to manage power consumption in a system is to coordinate the operation of the various clocks that have high power consumption.
The various components in a wireless device have different operating requirements for the clock signals used for their operation. Network devices generally require high-speed, high-accuracy clocks. However, these clocks consume large amounts of power due to the power required to create a high-accuracy clock and also that consumed while switching the clock drivers and clock network at high frequencies. Therefore, network devices typically have power saving modes which allow stations to enter a low-power mode when the stations are not accessing the medium. Specifically, if the device is not transmitting or receiving, it is possible to conserve power by generating a lower frequency and lower accuracy clock signal which suffices to meet certain system requirements. Even in these low-power modes, however, it is important for the network that the device maintains its high-accuracy timers.
It would be desirable, therefore, to provide a wireless device having a power management system capable of conserving power by controlling the clock generator to provide different clock signals that are matched to the specific operational requirements of the system at any time. One solution employed by many existing systems is to disable the high-speed, high-accuracy clock to put the network in a low-power mode. However, this approach creates a number of potential problems. For example, network devices need to maintain high accuracy timers even when operating in a low-power mode. Also, other agents may attempt to interact with the device when it is not being clocked, requiring complicated synchronization with those agents, or continuing to clock interfaces even when operating in low power mode. Furthermore, complicated hardware may be required to start up the high-accuracy clock when an external agent requires interaction with the network devices.
In view of the foregoing, it is apparent that it would be desirable to provide a wireless device having a power management system capable of conserving power by controlling the clock generator to provide different clock signals that are matched to the specific operational requirements of the system at any time, while also providing a means to maintain proper operation of the device when operating in a low-power mode.